1. Field of the Invention
This invention relates broadly to the field of electrical controllers, and in particular relates to a relay control circuit that provides highly reliable control for devices that perform in demanding environments such as space.
2. Brief Description of the Prior Art
Electrochemical relays have traditionally been utilized to control motors and other electrical devices. Electromechanical relays allow electrical devices with varying voltage and current requirements to be controlled with a standard voltage level such as from a switch panel. A controller that uses electromechanical relays in the conventional manner has important disadvantages for applications such as for use in space. First, the failure of an electromechanical relay or the device controlled thereby may result in the aborting of an important part of a space mission. For example, the failure of a motor which drives an actuator that unlatches a satellite for release from a spacecraft may prevent the satellite from being launched. Returning the satellite to earth results in a great waste of time and expense.
Another disadvantage of conventional controllers is that the failure of a single electromechanical relay or switch could result in premature performance of a time critical operation. For example, release of the satellite prior to full opening of the spacecraft cargo doors could result in serious damage to the spacecraft and satellite.
Finally, conventional controllers of motor driven actuators often use only limit switches to detect completion of the desired movement. The use of limit switches alone provides no short-circuit protection for the power source nor force-limiting protection in the event of obstruction of the actuator.
Accordingly, it is an object of the present invention to provide a highly reliable electromechanical relay control circuit that utilizes multiple levels of redundant function control.
It is a further object of the present invention to provide a safe electromechanical relay control circuit that requires the receipt of multiple control signals before time-critical operations are performed.
Finally, it is an object of the present invention to provide motor current sensing to detect full travel of the actuator driven by the motor being controlled as well as to provide short-circuit protection for the power source and force limiting protection in the event of obstruction of the actuator driven by the motor.